It is our purpose to understand how cellular systems by responding to environmental stimuli exercise genetic control over the synthesis and assembly of cellular membranes. Earlier support of this research effort has enabled us to provide a detailed model encompassing the roles of oxygen and light as these serve to regulate the synthesis of the photosynthetic membrane system of Rhodobacter sphaeroides. We have shown that oxygen and light are ultimately transformed to intracellular redox signals which directly control gene expression through the actions of new global regulatory proteins. Using genetic, molecular and biochemical approaches our model serves as the basis for the four specific aims presented here. These involve a biochemical delineation of the mechanisms through which the cbb3 terminal oxidase is able to configure the functional status of the Prr two-component activation system. We will test our hypothesis that anaerobic electron flow is used to post-transcriptionally control the functional state of this membrane system, as well as directly and indirectly regulate a diversity of gene expression profiles heretofore not recognized. We shall extend our analysis of the cbb3 oxidase to the roles of the individual subunits of the cbb3 oxidase in regulatory gene expression profiling and the role of each subunit in anaerobic electron flow and hence, gene expression. We shall examine how anaerobic electron flow is used to maintain the cellular levels of spheroidene and spheroidenone and how this ratio can be used to measure anaerobic electron flow through the cbb3 oxidase. Finally, using our Gene Chip we will be able to address the hypothesis that aerobic and anaerobic electron flow are the source of new intracellular signals which serve to regulate extensive gene expression profiles not heretofore explored. It is likely, that these studies will serve as a guide to the potential role of the electron transport chain in gene regulation in higher organisms.